Photochromic glasses are glasses whose lenses develop color quickly and serve as sunglasses when exposed to light including ultraviolet such as sunlight outside and lose color and serve as ordinary transparent glasses when exposed to no such light inside. In recent years, demand for the photochromic glasses are on the increase.
As methods for producing a plastic lens having photochromic properties, a method (hereinafter referred to as “impregnation method”) of impregnating the surface of a lens having no photochromic properties with a photochromic compound, a method (hereinafter referred to as “coating method”) of forming a layer having photochromic properties (photochromic coating layer) on the surface of a plastic lens, and a method (hereinafter referred to as “kneading method”) of obtaining a photochromic lens directly by dissolving a photochromic compound in a monomer and polymerizing the mixture are known. Of these methods, the coating method has an advantage over the other two methods in that in principle, it can impart photochromic properties to any lens substrate easily. For example, in the impregnation method, it is necessary to use a soft lens substrate in which a photochromic compound can be diffused easily, and in the kneading method, it is necessary to use a special monomer composition so as to develop good photochromic properties. Meanwhile, the coating method is free from such a restriction with respect to substrates.
Thus, it can be said that the coating method is an excellent method as a method for producing a photochromic plastic lens. However, a technique for forming a photochromic coating layer which has-satisfactory adhesion to a substrate and to a hard coat layer that is formed on the photochromic coating layer as required and develops good photochromic properties is not yet established.
Heretofore, as the coating method, (i) a method comprising coating the surface of a lens with an urethane oligomer in which a photochromic compound is dissolved and curing the applied oligomer (refer to the pamphlet of International Publication No. WO98/37115), (ii) a method comprising dissolving a photochromic compound in a polymerizable monomer composition comprising a combination of monofunctional, difunctional and polyfunctional radical polymerizable monomers, applying the composition to the surface of a lens and curing the applied composition (refer to U.S. Pat. No. 5,914,174), (iii) a method comprising dissolving a photochromic compound in a monomer composition comprising a combination of at least two difunctional (meth)acryl monomers only, applying the composition to the surface of a lens and curing the applied composition (refer to the pamphlet of International Publication No. WO01/02449) and (iv) a method comprising coating the surface of a lens with a composition comprising N-alkoxy methyl (meth)acrylamide, a catalyst (preferably an acidic catalyst) and a photochromic compound and heat-curing the applied composition (refer to the pamphlet of International Publication No. WO00/36047) are known. However, the above method (i) has problems that the temperature dependency of photochromic properties is high due to the low crosslink density of the obtained photochromic coating layer and that the photochromic compound is eluted into a hard coat solution when a hard coat is formed on the photochromic coating layer. Meanwhile, the methods (ii), (iii) and (iv) have a problem that adhesion between the glass lens substrate and the photochromic coating layer is not satisfactory.